Stain resisting alloys



Patented Jan. 24, 1939 UNITED STATES PATENT OFFICE 2,144,718 r STAIN RES] STING ALLOYS No Drawing.

Application December 18, 1930,

Serial No. 503,328

3 Claims.

This invention relates to alloys containing, as essential constituents, the metals iron, chromium, manganese, copper and nickel.

In an application bearing Serial No. 435,957, filed by me on March 14, 1930, patented August 8, 1933, Number 1,920,953 I have described alloys consisting essentially of iron, chromium and manganese; and I have shown that within the limits of composition given in the said application, the alloys combine deep-drawing properties with high resistance to staining and corrosion, and exhibit this combination of properties not only when quenched from temperatures of about 1000 C. to 1150 C. but also when air-cooled from like temperatures. The alloys discussed in my said prior application contain about 16%-22% of chromiurn; about 5%-15% manganese; and up to about 0.3% of carbon. When the carbon is below about 0.12% the alloys are especially soft and ductile, but not quite so strong as when the carbon is higher. In the case of the alloys in which high ductility is desirable, the carbon is to be regarded as an impurity, and the carbon content is determined by the fact that the cost of the metal increases as the percentage of carbon diminishes. In commercial operations the presence of some carbon cannot be avoided.

In an application Serial Number 444,876 filed by me on April 16, 1930, patented February 7, 1933, Number 1,896,154, it is disclosed that copper may be added to the alloys of my prior application giving new alloys with desirable properties. Such new alloys, when the copper content is suitably adjusted; are stain-resistant in approximately the same degree as the alloys of my prior application; and while the copper tends slightly to increase the hardness of the alloys, an appropriate addition of copper raises the Erichsen value and gives such a combination of physical properties as to indicate excellent deep-drawing qua1itiesan inference which isconfirmed by actual drawing tests.

By adding copper to the iron, chromium, manganese alloys of my prior application Serial Number 435,957 it is possible with a medium manganese content, say in the vicinity of 8%, to equal or, it seems probable, distinctly to surpass the drawing qualities obtainable without copper by incorporating a higher proportion of manganese. The invention therefore offers the possibilities of providing still better alloys than those described in my prior application, and of lowering the cost of the alloys by replacing a part of the manganese with the cheaper metal, copper.

Although I have done a large amount of experimental work on the new alloys, it has not been feasibleto test all possible compositions, and it is deemed unsafe in this field to permit the conclu sions to wander far from the experimental basis.

I therefore refrain from setting precise limits on the additions of copper which may be useful. Such limits are not of the essence of the invention, and in practice limiting values of the copper content would be avoided in view of the impossibility 15 in even the best metallurgical practice of working to precise limits. With this qualification it may be said that the useful copper range lies between the approximate limits of 0.25% and 2.5%. When the copper content is too high, the alloy 20 tends to become hot-short. With the manganese at 8% or less, the copper may rise to 2.5% and perhaps beyond, but with higher manganese percentages, in the vicinity of 14%, 2.5% of copper seems to be excessive, or at least not to be recommended. Alloys containing 3% of copper with as little as 6% of manganese were definitely hotshort, and broke up during forging.

As stated above, the chromium may be varied through about the range (16%-22%) given in my prior application, but my experimental work has been largely confined to compositions containing about 18% of chromium, it having been established in prior work with iron-chromium, iron-chromium-nickel, and iron-chromium-manganese alloys that a chromium percentage not far from this value is in most cases quite satisfactory, and found in the present investigation that about 18% of chromium is equally satisfactory in the copper-containing alloys.

The carbon percentages set out in my prior application, viz. not more than about 0.3%, and preferably not 'more than 0.12% are also recommended for the iron-chrornium-manganese copper alloys of deep-drawing quality. Where maxinium workability is not required, the carbon may rise to at least 1.0%.

The following tabulation shows the composition of specific alloys within my invention, and gives the numbers obtained in physical tests carried out on the respective alloys as quenched from 1050-1150 0.:

Alloy #3 is similar to #1 but contains 0.24% of carbon. The ductility is nevertheless excellent.

A: in the case of the alloys of application Serial No. 485,957 the chromium percentages which appear most promising fall between the approximate limits of 17% and 21%. Since the addition of copper permits the manganese percentage to be lowered, the preferred range for manganese in the copper-containing alloys is defined by the approximate limits 6% and 10%.

I have now discovered that by incorporating a sulltantial proportion of nickel, not less than 2%, with alloys of the type described above, the properties are still further improved; and certain of the resulting compositions are at least equal in workability and stain-resistance to the best comparable iron; or steels which have come to my attention. Accordingly, the present invention is an alloy containing iron, chromium, manganese, copper, and nickel.

As nickel is added to the iron, chromium, man- Baneae, copper alloys of my application Serial Number 444,878, the manganese content may be correspondingly lowered, but I prefer to have at least about 3% of manganese present. A chr0- mium content of about 18% is most favorable to the ductility of the alloy, and with such a chromium content, the sum of the nickel and manganese percentages should be at least 6%, and at least 8% if the ductility is to be raised to nearly its maximum value. Increasing the sum 01' the nickel and -1 beyond 14% does not, as a rule, improve the properties sufilciently to warrant the additional cost involved. When the chromium content varies much in either direction from 18%, the alloy tends to become less workable, a tendency which can be counteracted in some measure byadding more manganese and/or nickel.

'lhe following table shows certain of the physical properties of typical iron-chromium-manganese-nickel-copper alloys, and of comparable alloys free from copper. The alloys were prepared for testing by quenching them from 1150 C. Similar properties can be developed by air-cooling from temperatures within the range 1000 C. to 1150 C.

Alloy #4 may be regarded as alloy #2 with the copper omitted. The ductility is greatly lowered and the hardness is increased. Alloys #5 and #7 are copper-containing alloys respectively high and low in chromium, while alloys #6 and #8 are corresponding alloys free from copper.

The tendency of copper to produce hot-shortness is slightly diminished by the presence oi nickel, and with the most favorable composition, the alloys can be hot-worked when the copper content is as high as 2.75%. When hot-working is not contemplated, the copper may rise to 5%. The eflect of carbon is nearly the same in the nickel-containing and nickel-free compositions.

Iclaim:

1. A stain-resisting iron-base alloy having deep-drawing properties and comprising from about 16% to about 22% of chromium; about 0.25% to about 2.75% of copper; carbon, the carbon content being not more than about 0.3%; at least about 3% of manganese and at least about 2% of nickel, the sum of the manganese and nickel percentages falling between about 6% and about 14%; the balance of the alloy being substantially iron.

2. A stain-resisting iron-base alloy having deep-drawing properties and comprising from about 16% to about 22% of chromium; about 0.25% to about 2.50% of copper; carbon, the carbon content being not more than about 0.12%; at least about 3% of manganese and at least about 2% of nickel, the sum of the manganese and nickel percentages falling between about 8% and about 14%; the balance of the alloy being substantially iron.

3. A stain-resisting iron-base alloy having deep-drawing properties and comprising from about 16% to about 22% of chromium; about 0.25% to about 2.50% of copper; carbon, the carbon content being not more than about 0.12%; at

least about 5.3% of manganese and at least about 2% of nickel, the sum of the manganese and nickel percentages falling between about 8% and 0. 01; 0. 0. 24" 0. 05 0. 10 o. 13 7 0. 12 0. 11.15 18.54 Z 18.15% 18.30% 22.11% 2l.89 12.54; 11% 5.30% 0.54 6.27? 0.102 0.15% 11.20 0.1 o 5.917 4.31% 2.22% 4.38% 2.30 a 5.13% 5.88% 6.29 a 6.16 c 1.02% l. 10% 1.38% one 1.39% None 0.64 9 None 40' 40 45 42 41 4s 3s 30 100' 88.5 100 150 s0 11s The unit employed for expressing yield point and maximum stress in the above table is 1G!) lb. pc square inch.

Alloys #1 and #2 are low-carbon alloys embraced within the invention, #2 being low in nickel and proportionately high in manganese.

about 14%; the balance of the alloy being substantially iron.

FREDERICK M. BECKE'I. 

